This invention relates to retorting of hydrocarbons from solid feed material, and more particularly, to an improved surge bin for a flash pyrolysis process.
Flash pyrolysis has been applied to coal, oil shale, tar sands, and other solid feed materials to produce synthetic fuels. "PRODUCTION OF SYNFUELS FROM OIL SHALE, TAR SANDS AND COAL BY THE LR-PROCESS" by Dr. Hans J. Weiss, paper presented at the Synfuels First Worldwide Symposium, Oct. 7-9, 1981, (LR) Brussels, describes the Lurgi-Ruhrgas (LR) process. This process has been operated to carbonize coal, to crack crude oil, fuel oils, and naphtha into olefins and to produce synthetic fuel from oil shale, tar sands, and diatomaceous earth. In this process, the feed material is flash heated by circulating a solid heat carrier material through a mixer. The heat carrier is the feed residue which is produced in the process.
As an example, when oil shale is the feed in the LR process, a screw mixer mixes preheated raw shale, and hot spent shale. Retorting begins in the mixer. The solid material is transferred from a mixer to the surge bin where retorting continues. The surge bin provides a buffer for flow of solid material to a lift pipe in which the circulating solid heat carrier material is reheated and conveyed back to the mixer.
Prior art surge bins used in the Lurgi process do not promote uniform flow of solid material through the surge bin. Because of this, unretorted hydrocarbons can be carried to the spent shale combustion section and burned. The solid material in the surge bin may be self-fluidized from the evolution of hydrocarbons and there is considerable mixing in the bin. Because of this, some of the larger pieces of solid material may sink through the fluidized bed faster than the smaller particles. This results in significant solids bypassing, thereby reducing the yield of usable hydrocarbons.
It is an object of the present invention to promote uniform flow through the surge bin in an LR process.
It is another object of the present invention to improve the quality of the hydrocarbon product by reducing the amount of fine entrained solids in the oil.
It is another object of the present invention to provide gas or steam stripping in the surge bin to remove entrained hydrocarbons from the solid material and reduce residence time of the product vapors.